Automatic switch for use in telephone or like systems



April 18, 1939. R, TAYLOR ET AL 2,154,785

AUTOMATIC SWITCH FOR USE IN TELEPHONE OR LIKE SYSTEMS Filed Jan. 50, 1956 2 Sheets-Sheet'l April 18, 1939. R. TAYLOR ET AL 2,154,785

AUTOMATIC SWITCH FOR USE IN TELEPHONE OR LIKE SYSTEMS Filed Jan. 30, 1936 2 Sheets-Sheet 2 has E h 4 i T H BRA R hbg 85 4 m? 'l 7 {4 /'g F\ 10 hb7 J m f M [1m w v MW; L II GNR ---I Busv iv/z/vmas- (56/4 410 74 710/5 Patented Apr. 18, 1939 UNITED STATES PATENT OFFICE AUTOMATIC SWITCH FOR USE IN TELE- PHONE OR LIKE SYSTEMS Application January 30, 1936, Serial No. 61,442 In Great Britain February 8, 1935 12 Claims.

The present invention relates to automatic switches for use in telephone or like systems and is more particularly concerned with switches of the two-directional type adapted to hunt over a 5 group of lines distributed over a plurality of levels. The object of the invention is to provide an improved switch of this type in which the -peration is controlled in a simple and economical manner which readily permits changes to be l0 made.

According to one feature of the invention in an automatic switch of the vertical and rotary type for use in telephone systems after the switch wipers have been set in direct response to a train 15 of impulses hunting for an idle line is adapted to take place over a plurality of levels successively and after all the lines in a level have been found busy the next level to be hunted over is reached as a result of a level hunting operation.

According to another feature of the invention in an automatic switch of the vertical and rotary type for use in telephone systems hunting for an idle line is arranged to take place over a plurality of levels successively, and after all the lines in a level have been found busy the switch per forms a level hunting operation in search of a marking controlled by code signals transmitted over the switch wipers.

The invention will be better understood from the following description of one method of carrying it into eiiect, reference being had to the accompanying drawings comprising Figs. 1 and 2. These show a P. B. X final selector arranged to test two trunks simultaneously and adapted to perform a hunting operation over a number of levels successively.

Referring now to the circuit operations, when the switch is seized, a loop is completed across the negative and positive conductors so that relay A operates and at armature al energises relay B. Relay B locks by way of its armature bl, at armature b2 guards the circuit by placing earth on the release trunk conductor P and at armature b5 operates relay C. When the next digit is transmitted, relay A responds to the interrupfirst set of contacts in the level selected. On

the first rotary step the rotary oiT-normal springs are mechanically operated, thereby at springs NR2 removing the short-circuit from the righthand winding of relay C which therefore again operates. At the end of the rotary magnet stroke the associated springs rm close and complete a. circuit for operating relay E over its lower winding so that this relay at armature e2 opens the circuit of the-rotary magnet and at armature el completes a testing, circuit for the switching relays HA and HB to the test PI and P2 wipers respectively.

If both lines are busy, the wipers PI and P2 will fail to encounter battery so that neither of the switching relays can operate and hence when the rotary magnet has deenergised and released relay E, the magnet is again energised to advance the wipers a further step. As long as busy lines are encountered, interaction between relay E and the rotary magnet continues with the result that the wipers are rotated over the selected level in search of a free line. When a free line is found either relay HA or relay HB operates and opens the driving circuit for the rotary magnet to prevent further movement of the wipers. If two free lines are encountered simultaneously both relays HA and HB operate but relay I-IA has priority in that at armature hal it opens the looking circuit for relay HB which is therefore prevented from holding.

Assuming for the purpose of the description that relay HA operates, it will be seen that it looks over its upper winding at armature hal and at armature ha2 connects direct earth to the Pl wiper and test contact to guard the line selected and hold operated the cut-off relay in the subscribers line circuit. At armature ha3 the circuit for therotary magnet is opened, at armatures ha l and hail the ringing circuit is prepared by way of the upper set of wipers negative l and positive I, and at armatures hat and ha! relay D is connected to the spreaking conductors.

If relay HB had operated it would have performed precisely similar functions to relay HA except that the lower set of wipers negative 2 and posi- 56 tive 2 would have been connected up. The operation of the switching relay at either armature ha! or armature hbl opens the circuit for relay DR which releases after its slow period and at armature dr brings up relay J which at armatures 9'2 and 7'3 completes the ringing circuit including the generator GNR, upper winding of relay F and ringing return resistance During the ringing period ringing tone is extended from the common conductor III by way of the lower winding of relay D to the calling subscriber to inform him that the call is proceeding.

When the called subscriber replies, the direct current loop completed across the line causes the ring trip relay F to energise, whereupon by opening its light armature fl it locks up over its lower winding in series with relay HA. Relay F at armature f3 transfers the holding circuit of relay J to the control of its own armature a! and at armatures f5 and f6 cuts oil the ringing current and completes the talking circuit between the calling and called parties. Relay D now operates over the called subscribers loop in series with the iron-hydrogen current limiting resistance BRA. This resistance has the property of limiting the current passing therethrough to a predetermined value and its purpose is to maintain a constant battery feed to the called side of the circuit over a wide range of loop resistances. Relay D at armatures dl and (12 provides the usual supervision by reversing current to the calling side of the circuit and at armature d4 re-operates relay DR which locks. The operation of relay DR releases relay J and during the slow release period of the latter, booster battery is applied to the release trunk conductor P to operate the calling subscribers meter in the well-known manner. The arrangement of controlling the application of booster battery to the release trunk conductor by means of relay DR which is locked up obviates any danger of mul-,

tiple metering in case relay D operates intermittently due to clumsy removal of the receiver by the called party.

At the end of the conversation when the calling party replaces his receiver, relay A releases and allows relays B, C, F and HA or HR to fall away whereupon earth on the release alarm common H provides a self-interrupted driving circuit for the rotary magnet RM to advance the wipers clear of the banks so that they fall and restore to the home position where the circuit is opened by the off-normal springs N2. Relay B upon releasing, at armature b2 removes the guarding earth from the release trunk conductor P to enable the preceding switches to restore, but upon the release of relay C earth is re-applied to the release trunk conductor over armature 02 until the switch arrives at its home position where the circuit is opened by the off-normal springs N3. Under all conditions of release it is arranged that relay B de-energises relay C in the manner described and therefore the unguard period on the release trunk conductor is determined by the releasing time of relay C which is substantially constant. It should also be noted that seizure of the switch during the unguard period does not interfere with the release operation because the initial operating circuit of relay B is available only when the switch is in its normal position.

If all the lines in the level selected prove busy, the wipers are moved to the 11th position where cam spring S are mechanically operated thereby at springs Si opening the circuit for relay E and at springs S2 operating relay RN which locks over armature ml. Relay RN releases relay DR and prepares circuits for the code relays W, X, Y, Z Which are operated in various combinations as indicated in the lower right-hand corner of Fig. 2 and serve to bring about the release of the switch and control its movement to the next level of the P. B. X group, or alternatively, if the wipers have reached the end of the group, return a busy signal. The operating circuits for the code relays are completed over the 11th step multiple contacts associated with the banks negative l, positive I, negative 2, positive 2 which are earthed'in various combinations to cause the code relays to mark the vertical bank contact of the switch corresponding to the next level of the group to be hunted over. It is arranged that either relay W or relay X is operated for all combinations of the code relays other than that corresponding to the end of a group and therefore, when relay DR releases due to the operation of relay RN, the rotary magnet is energised in series with relay C to step the wipers to the 12th position from which they fall by gravity and restore below the banks to the normal position. I

When the normal position is reached, the circuit for the rotary magnet is opened at springs N2 and at springs N4 relay RN is released and a self-interrupted driving circuit is then completed for the vertical magnet VM in series with relay C so that the wipers are raised in search of the required level which is marked over the contacts of relays W, X, Y and Z.

When the marked level is reached, the interrupter springs vm of the vertical magnet are bridged by the low resistance left-hand winding of relay DR which thereupon energises in series with the magnet and locks over its other winding and disconnects the circuit to the magnet at armature (112 At armature drG the common locking circuit to the code relays is now opened so that they release and the normal driving circuit for the rotary magnet is also completed. The switch therefore hunts for a free line on the second level of the group and if all these lines prove busy the switch is again released and set to the third level of the group and so on.

If the whole of the lines in the P. B. X group prove busy, the wipers will eventually be moved to the 11th position on the last level where the code relays Y, Z are operated as suggested in the drawings. Busy flash and tone from the cam assembly ET is thereupon extended by way of the lower Winding of relay A to the calling subscriber to inform him that the connection required is busy. During the flash period of the busy signal when relay A is released, relay B remains held over its lower winding from the cam assembly BH to maintain the connection. When the calling subscriber replaces his receiver release of the switch takes place as previously described.

The 11th contact of the P2 bank on the last level of each P. B. X. group is connected to an overflow meter indicated by OF which is operated over armature m6 to record all overflow calls.

The metal rectifier MRA connected in circuit with relays HA and HB prevents operative connection between the PI and P2 wipers and also control points on the circuit are provided for the use of the maintenance staff.

For the purpose of ascertaining which set of wipers are in service it is arranged for armature hb8 on operation to prepare a circuit over lead I2 for a common buzzer which will sound when the appropriate test points T are linked together by the maintenance ofiicer if the second set of wipers is in use.

The lamp CSH is operated over lead l3 to give a delayed alarm if the calling subscriber omits to hang up at the end of the conversation.

We claim:

1. In an automatic switch, levels of bank contacts, lines terminating in said bank contacts, wipers having access to said lines by way of said contacts, means for operating said wipers in line hunting movements over a plurality of levels successively in search of an idle line, level selecting means directively controlled for operating said wipers to an initial one of said plurality of levels, means operated over the switch wipers in case all the lines in a level have been found busy for marking another level, and said level selecting means automatically operating said switch wipers in level-hunting operations in search of the marked levels.

- 2. In an automatic switch, bank contacts arranged in levels, Wipers having access to said lines by way of said contacts, means for operating said wipers in successive line-hunting movements over a plurality of different levels to search for an idle line, directively controlled means for operating said switch wipers in level-selecting operations, a group of relays, operating circuits for said relays, means including said switch wipers for completing said circuits in various combinations depending upon the potentials encountered by said wipers, and means including said relays for marking predetermined ones of said contact levels, thereby to automatically control said means for operating said switch wipers in level-selecting operations.

3. An automatic switch as claimed in claim 2 including means for stopping further level-hunting operations and for transmitting a busy signal in case said group relays are operated in a certain combination.

4. An automatic switch as claimed in claim 2 including overflow position contacts for each level engaged by said wipers after all the lines in a level have been found busy for completing said circuits in various combinations.

5. An automatic switch as claimed in claim 2 including means for releasing the operated group relays in response to the completion of a levelhunting operation and for reoperating said group relays in a different combination in case no idle line is found in the level selected in such levelhunting operation.

6. An automatic switch as claimed in claim 1 including means for directively operating the switch wipers in response to a train of impulses to select a corresponding level before the line or level-hunting means is effective.

7. An automatic switch as claimed in claim 1 including means for automatically restoring the wipers fully to normal after the line-hunting operation and before the level-hunting means is effective in case all the lines are found busy in the first line hunting operation.

8. An automatic switch as claimed in claim 1 including a motor magnet having a self-interrupting circuit for controlling the level-hunting operations.

9. In an automatic switch, bank contacts arranged in levels, lines terminating at said bank contacts, wipers having access to said lines by way of said contacts, means responsive to a. train of received impulses for directively operating said wipers to a position for testing the lines terminating at a predetermined level of said contacts, means for automatically operating said wipers over the contacts of said predetermined level to test the condition of said lines, other means for marking a second of said levels in the event all the lines terminating at the contacts of said predetermined level are busy, automatically operating means for fully restoring said wipers to normal in case all the lines terminating at the contacts of said predetermined level are busy, and said first-named means responsive to the restoration of said wipers to normal for automatically driving said wipers in a level-hunting operation until said marked second level is found.

10. In an automatic switch, bank contacts arranged in levels, lines terminating at said bank contacts, wipers having access to said lines by way of said contacts, means responsive to a train of received impulses for stepping said wipers to a position for testing the lines terminating at a predetermined level of said contacts, means for automatically operating said wipers step-by-step over the contacts of said predetermined level to test the condition of the lines terminating thereat, other means for marking a second level in the event all of the lines terminating at the contacts of said predetermined level are busy, automatically operating means for fully restoring said wipers to normal in case all of the lines terminating at the contacts of said predetermined level are busy, and said firstnamed means automatically operated for repeatedly stepping said wipers in a level-hunting operation until said marked second level is found.

11. In an automatic switch, banks of contacts arranged in levels, lines terminating in said bank contacts, a control contact in each of said levels, wiper having access to said contacts, means op erated in response to the impulses of an incoming impulse train for operating said wipers to the initial level for line-hunting movements over a plurality of different levels in search for an idle line, means for automatically operating said wipers in line-hunting operations, means operated through certain of said wipers when resting on a control contact for marking predetermined ones of said contact levels, and said firstnamed means automatically operating said wipers in level-hunting operations in search of the marked levels.

12. In an automatic switch having wipers and banks of contacts arranged in levels accessible thereto, control contacts in each level, means directively controlled for operating said wipers to an initial level, means for automatically operating said wipers over the contacts of a level, means operated through said wipers when certain of the control contacts are encountered thereby for marking predetermined ones of said contact levels, and said first-named means automatically operating said wipers in level-hunting operations in search of the marked levels.

REGINALD TAYLOR. GEORGE THOMAS BAKER. 

